ABSTRACT On October 8th, 2017, over a dozen fires erupted in northern California and produced damage on an unprecedented scale. Over 90,000 people were evacuated, 185 were hospitalized, 42 died, and over 5700 structures were destroyed. These fires were unusual not only in their scale and the rapidity of their spread, but also in that the vast proportion of affected areas were urban. Particular health concerns relate to toxic chemicals now widely used in building construction and interior furnishings, such as solvents, glues, metals, halogens, and formaldehydes; with high temperature combustion, an array of volatile organic compounds may be released. The different chemical composition of these wildfires compared with forest or grassland fires raises concern about potential health consequences. Additionally, similar to other disasters, emotional distress is widespread, and could have long-term emotional consequences for survivors including persistent post- traumatic stress symptoms and depression.1 Exposures to the toxic chemicals and stress, especially in combination, can also have serious long-term developmental consequences if delivered during critical periods during pregnancy. The goal of this R21 is to facilitate a rapid research response to this disaster that will collect biosamples and survey responses from individuals affected by the wildfires that can be used to determine contaminant exposure loads, mechanistic responses, and health biomarkers. We will use several strategies to collect biosamples and survey information from both untargeted and targeted individuals with wildfire exposure, including 1) a household-based community sample with door-to-door recruitment from a scientific sample of Census blocks; 2) a large convenience sample of volunteers for an online survey that agree to further studies; and 3) women who were pregnant during the wildfires. Further, we will conduct targeted analyses on a subset of 200 blood samples to examine internal exposure-related contaminants including chlorinated and brominated flame retardants using GC-MS/MS associated with varying degrees of fire smoke exposure and with reported health symptoms. We will also compare concentrations of these compounds found in blood with those found in air and ash samples. Finally, we will measure cortisol in hair to assess physical response to this stressful event and examine predictors of high hair cortisol from the survey. Achieving the aims of this proposal will help decision-makers understand and minimize the effects of future wildfires. Timely collection of samples and data from the diverse population exposed to these unprecedented wildfires will allow future investigations of short- and long-term human and developmental health effects of both chemical exposures and traumatic and stressful life events during and following the wildfires. With climate changes that predict increasing occurrence, duration, and intensity of wildfires,2,3 this will allow public health planning based on new understanding of internal exposures, mechanistic responses, and health biomarkers that result from these fires.